Babysitter Blues
by Garrae
Summary: "After all, how much trouble can two babies be? And they will be babies, because Beckett an' Castle can hardly go out for dinner in Manhattan as two black panthers. He can easily handle two babies." The giant O'Leary babysits the Castle twins. Another insane venture into the Cool for Cats universe. Two-shot. Caskett Cats #8.
1. Chapter 1

**Chapter 1: Sleep little baby**

"But Beckett…"

"Please, O'Leary? You're the only one we can trust."

"But Beckett…"

"They sleep really well, now. Honestly. You've been round lots, so you know that. And they take bottles last thing at night, and we'll have fed them their meal so you won't have to deal with the mess, and I'll leave you some milk ready, and we just wanna go out, you know? They're a year old now, and I keep worrying that they won't be synced to me any more and can you imagine what could go wrong?" She widens huge, pleading eyes at him. O'Leary, despite his long friendship with Beckett, is not proof against it.

"Waaaaallll," he drags out, longer than the Mississippi river, "I've been around enough they know me, and they're really cute – any way they come – an' I guess you deserve some grown up time."

"Thanks. I owe you."

O'Leary feels, after Beckett's left, that he might just have been hustled. He'd thought that she 'n' Castle had managed several brief nights out, but he guesses that they could do with a proper date night, an' if she's frettin' about the fluffballs gettin' a little more independent, then he supposes he can step up. After all, how much trouble can two babies be? And they will be babies, because Beckett an' Castle can hardly go out for dinner in Manhattan as two black panthers. He can easily handle two babies.

They are super-cute, he muses. Crawling like demons, in baby form, still small and fluffy as either feline. He tries not to think about the logistics of how they grow in any form, because it hurts his head. He reckons that it would hurt any head that didn't have the brains of Stephen Hawking, and he's none too sure about him either. Anyways, after the first three weeks, Beckett had stayed mostly human, and so the babies had too. Just as well. Half the NYPD seemed to have wanted to visit, though Castle had strictly controlled it, much to everyone's irritation, until he'd explained that waking Beckett would result in bullets.

O'Leary grins his sabre-tooth size grin. Castle's a good guy, and he's good for Beckett. If their twins grow up like them, they'll be pretty good stuff too. He turns back to his caseload, feeling just a little flattered that he's the only one trusted to look after the babies without their parents there.

A few days later, he gets a text from Beckett asking if the next Saturday night is okay. O'Leary's cool with that. Pete's out of town on some audit in Milwaukee, and takeout and the game isn't half as much fun on your own. _Sure_ , he sends back, _see you 6_.

When O'Leary gets to the Castles' loft (he supposes that if there are babies involved it's the Castles' loft), the twins are awake, happily exploring the floor, investigating the cushions, and trying to pull themselves up on the couch while squeaking joyfully if they achieve it. David is, as ever, close to his father; Petra is experimenting with head-butting one of the bigger floor cushions to see if it moves. Since Beckett is sitting on it, with an expression O'Leary can only describe as sardonic sappiness (it's very peculiar), it does not move. Petra is not impressed, and babbles at her mother with an edge of baby irritation that would prove her heritage without any need for DNA testing.

"They just get cuter and cuter," O'Leary drawls. The bass rumble attracts the babies' attentions. David claws at Castle's pants to stand up and survey the giant (Castle has a cautious palm around his middle), and blows a few baby bubbles at him. Petra, who has loved O'Leary since the moment he first picked her up as a tiny kitten and she tried to climb even before she could walk, crawls at near light speed to his feet and tugs sharply and demandingly at his jeans, emitting first a hopeful babble and, when that is not instantly answered, a more insistent noise accompanied by harder tugging. O'Leary bends down and sweeps her up, for which he receives a brilliant baby smile showing off a number of little white teeth.

"Waal, ain't you the sweet li'l thing when you get your own way," he coos. He can coo. It's just a bit more like a condor than a dove. Petra babbles at him some more. He sits down next to Castle and David and bounces her on his knee a few times. She takes a firm grip of his t-shirt and levers herself up. Castle looks a tad worried. O'Leary reckons that he's a little protective, but in deference to both Castle's worry and his likely death at the teeth and claws of one or other Castle-panther if either baby should be hurt, he uses one huge hand to hold both of Petra's and puts the other one firmly over her chubby diapered bottom. "Gettin' big, honeypie."

"Yeah," Beckett says. "They grow like weeds."

"That's what they're supposed to do."

"I guess. Every time I get home they've grown out their onesies again.."

"Not quite," Castle says. "But some days it feels like it." David squeaks at him from the floor, and Castle easily pulls him up to the same position as his sister. He gurgles. "That's right. Say thank you nicely."

"We really appreciate this, O'Leary," Beckett says.

"Where are you goin'? Just in case there's some real emergency."

"We'll both have our phones, but we thought the Fairway Café. I don't want to go anywhere too smart and noisy. I can get noisy right here at home."

"Oh, yes," Castle agrees fervently.

"Long way away."

"Yes, but it's good, and their pumpkin pie is to die for. Just what I want, really."

"I can make pumpkin pie," Castle says.

"Yeah, but good as that is, theirs is just a little better."

Castle humphs. David tries to copy it, and O'Leary grins widely. "Real daddy's boy, ain't he?"

"Yeah," Beckett says sardonically. "Pity me, O'Leary. Two of them to put up with."

"Waal, y'know, Beckett – he's got two of you. Your little Petra's gonna be just like you."

"That is not a reassuring thought, O'Leary!" Beckett squawks.

"And on that happy note," Castle says quickly, "let's show O'Leary where everything is and then go."

O'Leary duly learns where the bottles, diapers, spare onesies and cot (one cot, apparently the twins prefer to sleep cuddled together even when human, just as they would do as kittens) are; how to switch on the baby monitor (he reckons the switch marked _ON_ is quite a good clue); and is then directed to the fridge where there is an array of sodas and a full meal which looks very appetising and would feed three O'Learys. He is perfectly certain that Castle made it, largely because it's not Georgian food and that's all he's ever known Beckett to cook.

Finally Beckett and Castle have finished telling him everything three times over and pointing out the blindingly obvious four times, made him promise to call them if there is so much as a hiccup out of place, and leave, assuring O'Leary with every breath that the babies are really good sleepers now and he should put them down at around seven or so after they've each had their last bottle and don't forget to read them their story because it's important for their linguistic development, (that was Castle) but they won't worry too much if the twins have one slightly later night.

"Once they're asleep, they don't wake," Beckett assures him. "I don't know how we got that lucky, but it's pretty useful."

O'Leary shoos the two mother-hens out the door before they can delay any further and turns back round to the bright eyed babies.

"Looks like it's just you an' me," he rumbles.

If he could have heard Beckett's commentary to Castle, and seen Castle's stunned, lustful expression when she finishes, he might have been a little less sanguine. If he'd remembered that the Fairway Café is not far from Central Park, he'd have been a lot less sanguine. And if any of the three adults had remembered that felines are essentially nocturnal, they'd _all_ not have been sanguine at all.

O'Leary lowers his container-ship bulk to the floor, where the twins spend a great deal of quality time learning to mountaineer. He is, however, very grateful that the jeans are sturdy. A cup might otherwise have been required. They are not careful about where they grip. The babies squeak, babble and bubble at him pretty much constantly, and Detective Colm O'Leary, six-foot ten tall, fifty-four inch chest, with a buzz cut and muscles on his muscles, sharp shooter and best sparrer in the NYPD, lies on the floor cushions and babbles baby-talk right back. It is certainly the first time the babies have heard an evening's stream of baby-talk emitted down at the bassoon and double bass end of the orchestral scale. However, they like it, and they like him. Mountain climbing is obviously their favourite sport, and when O'Leary, totally besotted with Beckett's babies, props himself up a little with some more cushions, they practice on his chest.

After a while, however, and not too far after the twins' ostensible bedtime, their wide eyes (blue for David, hazel for Petra) begin to droop, and babble starts to change to whimpers. O'Leary, being really quite intelligent (he hides it: it's so useful to let people think that you're all muscle and no brain) heats up their bottles, and by dint of his sheer size is able to put David on one knee, Petra on the other, support them, one in each arm, and watch them both glug down their last bottle with sleepy relish. They are just so adorable, he thinks. He'd never have put Beckett down as maternal – and indeed, on most people's gauges she has effectively deceived them into thinking that she is not, having applied her own patent brand of sardonic commentary to most of the trials of parenthood, though O'Leary knows that she is fiercely in love with and ferociously protective of her twins – but even she has a small picture of Castle with both twins on her desk, and Espo tells him that when she looks at it her whole face softens.

He gathers up his two sleepy, mumbling charges, one against each shoulder, and takes them up to their cot. Just as he'd been told, they snuggle into each other. He looks around for their storybook, and spots it exactly where he ought to have expected it, on a table right next to the cot, next to which is a very comfortable armchair. He sits down, and begins.

"Out of the gate and off for a walk went Hairy McClary of Donaldson's Dairy," he reads in a singsong bass, picking up the rhythm without any difficulty and looking at a small Scots terrier with enough fur to qualify as a mobile rug; and carries on happily through Hercules Morse, as big as a horse; Bottomley Potts, all covered in spots; Muffin McClay like a bundle of hay; Bitzer Maloney all skinny and bony; and finally Schnitzel von Krumm with the very low tum. O'Leary's grin widens with every page and every new dog, though the only one he'd like to own is Hercules Morse, who just might be big enough to suit him.

By the time he's finished, the babies are, as promised, asleep. O'Leary takes the monitor, tiptoes out of the room without hitting his head on the doorway – for three years, between sixteen and nineteen, he'd had trouble with that – and sneaks silently downstairs to have the dinner that had been left for him. The babies don't make a single untoward squeak or snuffle as he eats it. Not wishing to push his luck, however, he doesn't turn on the TV, but selects a book from the extensive Beckett-Castle library, and settles down comfortably, keeping a wary eye on the monitor.

Around about nine or so, he hears a soft noise, but since it's not immediately repeated, he doesn't think anything of it. He's going to let sleeping babes lie. There is a small rustle, but it don't make no nevermind.

* * *

Over at Fairway Café, located at West 74th and Broadway, and therefore extremely conveniently placed for a late night feline excursion to Central Park (though Beckett has already twisted Castle's ear for reminding her not to eat the squirrels that she chases or they'll have another set of kittens and he's not sure the world can cope with a pregnant Beckett) Castle and Beckett are enjoying a very nice meal safe in the knowledge that O'Leary can cope with nearly anything.

So when Beckett breathes seductively, "I wanna go play, Castle," and curls her fingers, he's nothing loth. They saunter across to Central Park, look naughtily at each other, Beckett stretches slightly and dusts a kiss over Castle's mouth – and then changes to Onyx and slips through the entryway unseen by any other man or beast. Castle's behind her in a heartbeat. They strut through the grass until they're well away from any edges where people might see them, and then Castle nips assertively at Beckett's neck and they both shift into their panthers: Castle massive and powerful, Beckett slimmer and elegant: both of them a lethal streak of darkness in the New York night. They shake out their paws, and open up with a long, stretching chase. Beckett flirting her tail and encouraging Castle-panther to chase and catch her, cover her with his feline bulk and take her down. It's all very satisfying.

They sneak out of the Park as invisibly as they arrived, and start back to the loft.

* * *

 _Thank you to all readers and reviewers. Chapter 2 on Wednesday._

 _This is another instalment in the insane (and entirely fluffy) Cool for Cats universe, and therefore thinking too hard about the - er - science (really?) behind it is likely to fry the brain._

 _This story is firmly the fault of Shutterbug5269._


	2. Chapter 2

**Chapter 2: Don't you cry**

O'Leary picks up a more definite rustle from the baby monitor, followed by a funny little noise. It doesn't quite sound like the babies. This, he considers, is a matter that should be investigated. He sneaks upstairs as quietly as a mountain can sneak, and opens the bedroom door.

On balance, that was a major mistake. His eyes haven't really adjusted to the darkness before two enthusiastic small furballs have dived past his ankles and made a break for freedom. They're halfway down the stairs before he's reacted, and his first reaction is _not_ polite.

"Holy _shit_ , Beckett!" he wails. "Couldn't you have _told_ me you were plannin' on shiftin'?"

The kittens stop their helter-skelter escape at the bottom of the stairs and look, wide-eyed, back up at the unusual sight of a wailing mountain. Then they meep at each other, one bats the other and takes off, and suddenly there are two mischievous little fluffballs skittering around the wooden floors and sliding into the cushions because they haven't quite learned how to stop. O'Leary follows them down and wonders what the hell he is going to do now.

He hasn't quite decided about that when there are two odd small sighing noises and the kittens are suddenly panther cubs. Still adorably cute and fluffy, but he's none too sure how he feels about the rather more obvious teeth and claws.

"Beckett," he says to the empty air, "you an' me are gonna have _words_." Suddenly it's all become horribly clear. Fairway, O'Leary remembers, is near enough to Central Park. Aw, _hell_. His one consolation is the amount of fun he is going to have embarrassing the crap out of both of them. He doesn't think either of them had thought that the babies-kittens-cubs would have woken when their parents shifted. One thing's for sure, though, they're still synced.

Dammit.

He looks at the two cubs play-fighting – he hopes it's play, because one of 'em's got a damn good grip on the other's ear – aw, _no!_ It's crying. He separates them, and pets the crying one. He guesses it's David, if only because the other bears an extraordinary (even if feline) resemblance to an embarrassed Beckett (not that he or anyone else sees that very often). He cuddles and pets David till he's happy again and emitting something that might be a baby purr, and picks up Petra.

"You," he says firmly, "are a naughty girl." He taps her gently on her ebony nose. "You're not to hurt your brother." She mews at him. It doesn't exactly sound like she agrees. He taps again. "You just stay right here in time-out for a minute." _That_ was quite definitely an attempt at a growl, last heard when Beckett realised he knew what they were. He hangs on to Petra – not being stupid – in a way that ensures her small but sharply gleaming claws are not in contact with him. "Nope. You don't get to scratch me." She yawns, and shows off pointed teeth. "Or bite. You just behave."

A minute later he puts her down. Two minutes later they're fighting again, though there is no ear biting. O'Leary settles himself down on the floor with them and makes sure that there is no real violence, separating them cautiously and only occasionally getting scratched. He's got this. He'd prefer it with a pair of tough gloves, but he's got it. They are so cute he'll even forgive them the scratches.

After a bit he thinks he really ought to put them back in the cot, an' maybe they'll go to sleep. It'll give him time to tidy up a bit.

David is quite happy to be picked up. Petra, on the other hand, thinks that it's a lovely new game from her favourite giant. She mews happily and slithers herself round the floor, evading his huge hands. David spots her playing chase and starts to squirm and wriggle too. O'Leary, scared to hold him too tightly because so many things, such as cups and people, turn out to be rather depressingly fragile when he grips hard, puts him down, and then watches with utter horror as the two cubs take off for Castle's office. He is damn sure they're not allowed in there. It's full of breakables.

About that point, he discovers that even panther cubs are a lot faster across the floor than he is. Size is not always an advantage, especially when you start from a prone position. Fortunately, the cubs tear straight through the office and – oh _crap_ – straight into somewhere O'Leary has absolutely no desire ever to see, being Beckett and Castle's bedroom. There are some things to which even friends should never be subjected. Ever. Beckett is going to owe him a Great Lakeful of beer. He contemplates the joy of revenge, for an instant, and wonders whether telling Esposito that Beckett's nickname used to be _butterfly_ would suffice. (Not pretty fragile things. No. Think Muhammed Ali type butterfly.) He decides that it would be a good start, and, extremely reluctantly, follows the cubs.

Even more fortunately, there is nothing in the Castle-Beckett bedroom to sear his eyes and make him need to scrub his brain. (He is also very firmly not thinking what two full-grown panthers might be doing in Central Park, because he just _knows_ he won't like any of the possible answers, and he doesn't really want to have to arrest his pals. Central Park is, after all, _his_ precinct.) He doesn't look at the tall wooden post more than once, clocks the deep scratches, shudders at the still-crystal clear memory of Beckett's claws over his femoral artery, and follows the kits into the bathroom. He shuts the door.

In less than half a minute, the bathroom has become chaos incarnate. David is tugging very hard at the toilet roll, in which he has wound himself and can't get free. He isn't pleased. On the other hand, he is immobilised, temporarily, which O'Leary thinks is an unexpected bonus. He picks up the mummified David and in default of any other safe place plops him in the bath. One naughty cub dealt with, he can concentrate on Petra. She's sneaky, and the bathroom is not small.

O'Leary sits down, folds his arms, and waits. He's really hoping that not playing will make Petra come to see why not. Reverse psychology. It works on her mother. Sometimes.

A small black nose pokes out from behind the sink pedestal. O'Leary looks bored. It's followed by some whiskers, and then a little black furry face. O'Leary re-crosses his arms, and turns away. Petra mews, loudly and demandingly. David wails from the bath as he finds that he can't get out. O'Leary ignores both of them, except for taking a quick snap of David to amuse the cubs' parents and show to any later girlfriends which David might have (should stop him having as many as Castle is reputed to have had).

Petra lays her ears flat in an extremely irritated fashion reminiscent of her mother (O'Leary thinks with malicious satisfaction that Beckett is going to have hell to pay trying to control her, and considers this to be perfectly fitting), and manages a respectable effort at a juvenile growl. The rest of her emerges, stalks towards O'Leary, and, when he continues to ignore her, jumps into his lap, bares her teeth, runs out her claws – and finds herself picked up in the same way as earlier and as a result is pathetically squeaking in disgust.

"Gotcha, troublemaker," he grins at Petra, who is vocally unappreciative, and follows up by plucking David out of the bath, still swathed in most of a roll of expensive toilet paper. Eventually David works out that claws and teeth will defeat the wrappings, and manages a certain amount of extrication. A small white tuft continues to adorn one ear.

O'Leary exits the bathroom, bedroom and office with the cubs dangling bonelessly, one from each giant hand, mewing miserably at being deprived of their fun, shutting each door firmly behind him, and then plonks his enormous self back down on a cushion. He glares at the cubs. David meeps cutely, and tries to look adorable. Petra glares right back at him. O'Leary detects a considerable resemblance to their parents. He does not detect any resemblance to sleepiness, and sighs. The cubs' fur ripples. He glares some more, which has no greater effect.

"You," he says generally, "are a pair of troublemakin' terrors." They appear to regard this as a compliment. "You should be asleep." This does not find favour either. "It's not playtime." They both make cross little growly noises. "You're both goin' back to bed." Larger growly noises, and a certain display of teeth and claws. "That won't work on me," O'Leary points out. "Your mommy's gun don't work on me, and you two ain't nearly as scary as her." They mew. He expects that it's vehement agreement. "Bed," he says firmly. "Now."

Upstairs, he puts on a nightlight, turns back now he can see and shuts the door firmly behind him, and then puts the two cubs into the cot. A second later they are kittens. The fluff-ball kits make an escape attempt. O'Leary puts them back. They try again. He puts them back, again. They try a third time – and he catches them mid-jump just before there's another sigh and he has two very cross, tired babies wailing loudly at him. He can't help tucking them against his broad shoulders, and patting them very gently. The wails diminish, and then cease. He puts the two little forms back into their cot, where they snuggle together and appear to be asleep again, and vacates, switching off the nightlight, as silently as he can, breathing a sigh of relief.

Downstairs, O'Leary decides that the cushions are no more untidy than when he arrived, and declines even to consider any form of tidying of the bathroom. He is not going through the bedroom ever again. He flumps down on the couch, regards the sheddings of kitten and panther fur on his jeans with a sigh, and wonders where he can find either several beers or Castle's whiskey. He deserves it.

At that inapposite moment, the door opens and the reprobate couple enter. They look extremely self-satisfied and they have _definitely_ been up to some very adult mischief.

"Hey, O'Leary," Beckett says, followed by Castle's pleased rumbles. "All okay?"

O'Leary casts her a dyspeptic glance. "While you two have been makin' mischief all over Central Park – an' don't bother denyin' it, because I know you have" – Beckett blushes guiltily, and Castle's ears colour though he's sporting a very smug smile – "you forgot that cats are nocturnal."

"Big word, O'Leary. Do you know what it means?" Beckett tries to divert.

"Sure I do. It means that they _wake up at night and want to play_." He sounds like the arrival of an avalanche.

Beckett sits down hard. Castle stares at him. "They woke up?" Castle says faintly. "Oh my God."

"We never thought of that," Beckett adds. Her blush brightens.

"Um… what happened?"

"I went up to investigate a strange noise and the kittens came sailin' out, hit the stairs before I could catch 'em" –

"They can't do stairs yet."

"You think? They did them pretty fine tonight."

"They could've been hurt!" Castle says. "How did you let them escape?"

"How did _you_ not tell me you were plannin' on shiftin?" O'Leary bats straight back. "Least then I'd've expected furballs not babies!"

"So they got down the stairs – Hell, Castle, that means we need to get a stairgate. With mesh so they can't sneak through." –

"Never mind your domestic logistics now, Beckett. You left me with the furry terrors. I guess that's when you pair shifted to panther, 'cause suddenly I got two fighting cubs. Petra bit David."

"Nothing new. D'you tell her off?"

"Sure. Tapped her nose and gave her time out."

"'Kay."

"So they messed around for a bit – no more bitin', but that girl of yours fights _dirty_ " –

"She comes by that honestly," Castle mutters, not quite quietly enough, and squawks as Beckett twists his ear –

"an' then they took off for your office." Castle emits a very strange strangulated wail-scream. "Went straight through, through your bedroom" –

"They are _not allowed_ in there!" Beckett says crossly. "Not without us."

"Tell them that," O'Leary mutters dryly. "Anyways, they ended up in your bathroom. You can tidy that up," he adds, unabashed. "Your boy liked the end of the paper. Wrapped himself right up in. I took a photo."

He displays the photo. The parents of the small Nemeses snigger evilly.

"That's one for the album when he gets his first girlfriend," Castle says.

"Really?" Beckett says wryly. "How exactly were you planning to explain to her that he was a panther kitten?"

"Oh." He droops. "Keeping this secret is so not cool," he complains.

"Damn right," O'Leary says. The other two glare at him.

"Look, we're really sorry. I never thought they would wake up," Beckett apologises.

"Yeah."

"Next time, take them with you."

"We would do, but they'd run off in the Park and we'd lose them. I don't wanna spend all night trying to find them."

" _I_ don't wanna spend all night dealing with them throwing up because they've eaten the squirrels," Castle says wickedly.

"Shut up, Castle."

"Squirrels?" O'Leary asks. Even for Castle that's a little random.

"Trust me, you don't wanna know about the squirrels."

But O'Leary's intelligence has taken a few leaps. "You guys chase and eat the _squirrels_? Man, that's cold. They're cute."

"Would you prefer we ate the people?" Beckett enquires, acidly.

"Waal, no," he admits. "But Beckett, squirrels are _cute_."

"And they give Beckett tummy upsets," Castle says. "Which is why we have" –

"Shut up, Castle." Beckett gives him a deadly glare. He shuts up, rather too late.

O'Leary grins, very widely. "I get it," he says. "Bit unplanned, those twins?"

Beckett grumbles into thin air. Castle looks conscious.

"Let's have coffee," Castle tries. "O'Leary, wanna drink? I think you might need one, and if you don't need it you sure deserve it."

"Yeah," he rumbles. "I think I do." He pauses, as an idea occurs to him. "You could always make them little harnesses and leads. Or buy them at the pet store. Like for small dogs. That way you could take 'em with you. You could hold the lead in your teeth."

The other two regard him as if he's crazy.

"But O'Leary," Beckett says saccharinely, "that would spoil all your fun, next time round." He raises a caterpillar-eyebrow. Beckett holds his gaze right back. "After all, you did a great job. You're very cool with cats."

 **Fin**

* * *

 _Thank you to all readers and reviewers. Much appreciated, especially guests whom I can't thank directly._

 _Hawkie - thank you for the round up review. Always appreciated._

 _Next up, the M- rated Choices, as a reply to several people who were worried about how Castle became a shapeshifter._

 _Suggestions in this insane, fluffy universe welcome, and if they spark inspiration then I'll write them._


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